Radar protection device for wireless networks

ABSTRACT

A method for radar protection. The method includes recording energy events and calculating differences in recorded energy events to determine pulses. The method further includes sorting intervals between pulses into histogram bins, each bin representing a range of time intervals between two pulses, each pulse indicative of a radar frequency and limiting network traffic on a frequency based on a selected bin count.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/910,682, filed on Aug. 3, 2004 now U.S. Pat. No. 7,230,566.

BACKGROUND OF THE INVENTION

The present invention relates generally to wireless networks and moreparticularly to a radar protection device and method for wirelessnetworks.

Current and projected growth for unlicensed wireless devices operatingin a frequency band located at approximately 5 Gigahertz has promptednational and international regulatory bodies to promulgate regulationsthat ensure that interference with incumbent systems is minimized. Suchunlicensed wireless devices generally use packeted data and include, butare not limited to, wireless devices in accordance with the Institute ofElectrical and Electronics Engineers (IEEE) 802.11 standard. More oftenthan not, such regulations are, in part, due to military and weatherradar operations ordinarily conducted within the band. Generally, theoperation of more unlicensed devices within the band increases theopportunity for interference and raises the noise floor of the band,potentially compromising the operational performance of military andweather radar systems.

For instance, both the European Telecommunications Standards Institute(ETSI) and the Federal Communications Commission (FCC) have publishedrequirements for radio local area network (RLAN) devices that operate inthe Unlicensed National Information Infrastructure (U-NII) frequencybands between 5.250-5.350 and 5.470-5.725 Gigahertz. Further, thedevices are required to employ a mechanism that allows the devices toshare the spectrum with radar operations, notably military and weatherradar operations, in such a way that the devices do not interfere withradar operations.

Short of the required sharing of the spectrum, one approach reports ameasurement summary in a radio communications system. More specifically,once a mobile station within a system is tuned to a selected frequencyrange, a measurement is made of communications energy. If communicationsenergy is measured or detected, the energy is decoded to determinewhether the communications energy contains packeted data. If packeteddata is detected, further analysis of the data packet is conducted todetermine whether the packeted data is in accordance with the Instituteof Electrical and Electronics Engineers (IEEE) 802.11 standard. If it isdetermined that the packeted data is 802.11 packeted data, a measurementsummary field is populated with a value indicating the frequency rangeto which the mobile station is tuned. Otherwise, an indication is madethat 802.11 packeted data is not being communicated on the frequencyrange to which the mobile station is tuned. The approach uses a rathercomplex delay correlation method for such determinations. Although thisapproach reports a measurement summary for a mobile station inclusive ofwhether or not communicated energy on a particular frequency is 802.11packeted data, the approach fails to provide a radar protection systemfor wireless devices that allows the co-existence of a wireless networkwith radar systems.

However, another approach does allow the co-existence of a wirelessnetwork with radar systems. More specifically, this approach providesradar detection and dynamic frequency selection for wireless local areanetworks. Further, this approach includes a radar detection process thatperforms a frequency domain analysis of an incoming signal to derivephase and magnitude information, the output of which is binned into 52bins of 300 kilohertz. The bins are analyzed to identify and distinguishamong different types of radar such as continuous wave tone radar andchirping radar in which the pulses are swept across a frequency range.With radar, the power is typically concentrated in one of the bins, orat a specific frequency.

This approach also provides analysis of a packet to determine whetherthere are any spikes within the packet above a certain threshold, as aspike might indicate a radar signal. The amplitude and duration, i.e.,pulse width, of the spike is analyzed to determine whether or not thespike is indicative of a radar signal. Spikes within the packet may betime-stamped so that the spike can be treated as a new or separateevent.

This approach also determines the period of a signal once a particularevent is determined to be a radar signal through a frequency domainanalysis of the length and magnitude of the event. Similarly, afrequency domain analysis is used to determine the period of a signal.

Particularly, this approach uses the forgoing radar detection process atan access point, and if the access point detects the presence of a radarsignal, the access point changes channels. Despite providing a radarprotection system for wireless devices that allows the co-existence of awireless network with radar systems, the radar detection processassociated with this approach is of limited utility. Foremost, the useof Fast Fourier Transform, Discrete Fourier Transform, or time domainanalysis is particularly burdensome. All of these types of analysisrequire significant computational and processing capabilities. Moreover,such processing can take a considerable amount of time. Further,capabilities inherent in current access points are generallyinsufficient to allow the use of such types of analysis. Therefore, manyexisting access points are not capable of using analysis processesassociated with this approach.

Thus, there exists a need for a radar protection device and method thataddresses the regulatory requirements and allows the co-existence of awireless network with radar systems.

SUMMARY OF THE INVENTION

The present invention addresses regulatory requirements and allows theco-existence of a wireless network with radar systems. More particularlythe present invention scans for the presence of radar signals and, upondetection, limits transmissions of the wireless network device on thesame frequency, thereby reducing interference with and protecting theoperation of radar systems.

In accordance with the present invention there is disclosed a method forradar protection. The method includes recording energy events,calculating temporal differences in recorded energy events to determinethe presence of pulses, sorting intervals between pulses into histogrambins (each bin representing a range of time intervals between twopulses, and each pulse indicative of a radar frequency), and limitingnetwork traffic on a frequency based on a selected bin count.

Further in accordance with the present invention there is disclosed aradar protection device. The device includes a receive antenna and areceiver circuit configured to record energy events and a controllercoupled to the receiver circuit and configured to execute program codethat allows co-existence with radar systems. The program code includesinstructions that command the controller to calculate temporaldifferences in the recorded energy events to determine the presence ofpulses and sort intervals between the pulses into histogram bins, eachbin representing a range of time intervals between two pulses, eachpulse indicative of a radar frequency. The device further includes atransmit antenna and a transmit circuit coupled to the controller. Theprogram code further includes instructions that command the controllerto cause the transmit circuit to limit network traffic on a frequencybased on a selected bin count.

In one aspect of the present invention, a computer-readable medium ofinstructions for radar protection includes means for recording energyevents, means for calculating temporal differences in recorded energyevents to determine the presence of pulses, means for sorting intervalsbetween pulses into histogram bins, each bin representing a range oftime intervals between two pulses, each pulse indicative of a radarfrequency; and means for limiting network traffic on a frequency basedon a selected bin count.

By virtue of the foregoing, there is thus provided a radar protectiondevice and method that addresses the regulatory requirements and allowsthe co-existence of a wireless network with radar systems.

These and other objects and advantages of the present invention willbecome readily apparent to those skilled in this art from the followingdescription wherein there is shown and described a preferred embodimentof this invention, simply by way of illustration of one of the bestmodes suited to carry out the invention. As it will be realized, theinvention is capable of other different embodiments and its severaldetails are capable of modifications in various obvious aspects allwithout departing from the spirit of the present invention. Accordingly,the drawings and descriptions will be regarded as illustrative in natureand not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the presentinvention and, together with a general description of the inventiongiven above, and the detailed description given below, serve to explainthe principles of the present invention.

FIG. 1 is a block diagram of a radar system and wireless local areanetwork including a number of access points in accordance withprinciples of the present invention;

FIG. 2 is a graphical depiction of a typical radar signal transmitted bythe radar system shown in FIG. 1;

FIG. 3 is a functional block diagram of a portion of a typical accesspoint in accordance with principles of the present invention;

FIG. 4 is a graphical depiction of a typical signal indicating theoperation of the access point shown in FIG. 3;

FIG. 5 is a temporal plot of the operation of the access point shown inFIG. 3;

FIG. 6 is a histogram of the pulse intervals shown in FIG. 5;

FIG. 7 is a functional block diagram of an access point in accordancewith principles of the present invention; and

FIG. 8 is a flowchart illustrating the program flow of a method for aradar protection device for the access points shown in FIGS. 1, 3, and7.

DETAILED DESCRIPTION OF THE DRAWINGS

Turning to the Drawings, wherein like numbers denote like parts, FIG. 1shows a wireless local area network 100 configured to provide wirelessdata communications with a mobile station 102. Further, wireless localarea network 100 and mobile station 102 operate in accordance with theInstitute of Electrical and Electronics Engineers (IEEE) 802.11 standardin a frequency band located at approximately 5 Gigahertz. Morespecifically, wireless local area network 100 operates in accordancewith requirements published by the European Telecommunications StandardsInstitute (ETSI) and the Federal Communications Commission (FCC) forunlicensed wireless devices that operate in the Unlicensed NationalInformation Infrastructure (U-NII) frequency bands between 5.250-5.350and 5.470-5.725 Gigahertz. Further, wireless local area network 100includes a radar protection device that allows the network to share thespectrum with radar operations, e.g., military and weather radaroperations, in such a way that the network does not interfere with theradar operations.

To this end, wireless local area network 100 includes one or more accesspoints 104 a-n, where “n” denotes any practical number of access points.Access points 104 a-n are advantageously interconnected using a fixedbackbone network 106. As shown and in operation, packeted data iscommunicated using a wireless link 108 between mobile station 102 and aselected access point 104 a. More specifically, packeted datatransmitted by access point 104 a to mobile station 102 using wirelesslink 108 is transmitted on what is commonly referred to as a forwardlink channel, while packeted data transmitted by mobile station 102 toaccess point 104 a is transmitted on what is commonly referred to as areverse link channel.

Those of ordinary skill in the art will appreciate that access points104 a-n can also advantageously be dedicated to or used as a bridge. Ina bridge application or configuration, an access point 104 a-n isprimarily dedicated to wirelessly communicating with another accesspoint. In such a configuration, an access point 104 a-n typically uses adirectional antenna aimed or pointed at the other access point toprovide additional gain and selectivity. An access point 104 a-nconfigured as a bridge generally does not communicate with a mobilestation 102. Thus, the present invention is not limited to access points104 a-n that communicate with mobile stations; but rather, includesaccess points configured as bridges.

In the Unlicensed National Information Infrastructure (U-NII) frequencybands frequency bands between 5.250-5.350 and 5.470-5.725 Gigahertz,forward and reverse link channels are not assigned to particularsystems. In other words, wireless local area network 100 is not assigneda portion of the frequency band(s) for its exclusive use. Rather,wireless local area network 100 must share the frequency band(s) withother concurrently operated systems, notably radar systems. Radarsystems include, but are not limited to, military and weather radarsystems ordinarily operated within the band(s), an exemplary radarsystem being shown at reference numeral 110. To prevent simultaneoususage of the same portion of the frequency band(s), a dynamic frequencyselection scheme is to be utilized by a system operating within theband(s) according to current published requirements by both the FederalCommunications Commission and the European Telecommunications StandardsInstitute.

Generally speaking, in a dynamic frequency selection scheme, channelswithin the band(s) are dynamically selected for use based upon whetheror not the channel is being used by another system. More specificallyand in accordance with one aspect of the present invention, if a channelis being used by a radar system, e.g., radar system 110, access points104 a-n select another channel for data communications. Furthermore,when using a dynamic frequency selection scheme in accordance withteachings of the present invention, the same channel is not used by botha radar system 110 and a wireless local area network 100.

Radar signals are characterized by bursts of periodic pulses of radiofrequency energy. These pulses are distinguishable from wireless networktransmissions due to their periodicity and relatively short pulse width.The number of pulses and the period of time between the pulses vary fordifferent types of radar. Despite this variation, the number of pulsesand the period of time between the pulses may be parameterized.Referring to FIG. 2, an exemplary radar signal 200 transmitted by radarsystem 110 of FIG. 1 is shown. Radar signal 200 comprises a series ofpulses 202 received in a series of bursts, two bursts of which are shownat reference numerals 204 and 206, respectively. The bursts 204, 206 areseparated by a period of time generally indicated at reference numeral208. Each pulse 202 represents a high frequency, i.e., approximately 5Gigahertz, sine wave or modulated wave having a pulse duration or pulsewidth (PW) of approximately one to twenty microseconds. However, pulsewidths of several hundred microseconds are known. The period of timebetween the start of consecutive pulses is referred to as the pulseperiod and is the inverse of the pulse repetition frequency (PRF),designed as (1/PRF). The burst length (BL) is the number of pulses 202in a burst 204, 206 or, equivalently, the time taken for a burst 204,206 of pulses 202. The burst interval (P) is the time taken between twoequivalent reference points in two consecutive bursts 204, 206, andtypically is between approximately 1-60 seconds.

Thus, as illustrated in FIG. 2, radar signal 200 is characterized byperiodic pulses and periodic bursts and is parameterized accordingly. Itwill be appreciated by the skilled artisan that radar signal 200exemplifies a rotating radar signal and that a tracking radar signalwill not appear as periodic busts. However, the present invention alsoapplies to tracking radar signals using the periodicity between pulses.Referring to FIGS. 1 and 2, and in accordance with an aspect of thepresent invention, the periodic characteristics of radar signal 200 areused by wireless local area network 100 to identify transmissions from aradar system 110. More specifically, access points 104 a-n withinwireless local area network 100 are configured for radar protectionthrough the inclusion of a radar protection device.

Turning to FIG. 3, a block diagram of a receiver portion of a typicalaccess point 300 (e.g., access points 104 a-n illustrated in FIG. 1)configured in accordance with principles of the present invention isshown. As shown, access point 300 includes a receive antenna 302 coupledto a bandpass filter 304 and a low noise amplifier 306, for receivingpacketed data on a reverse link channel. Access point 300 furtherincludes a mixer 308 and an associated local oscillator 310 responsiveto a controller 324, coupled to low noise amplifier 306 for tuning to orselecting a receive frequency or channel. A series of bandpass filters312, 316 and amplifiers 314, 318 are coupled to mixer 308 andanalog-to-digital converter 322, and complete a receive path 338. Inaccordance with an aspect of the present invention, receive path 338 isused to detect radar signals.

As also shown, an 802.11 physical interface controller 334 comprisesanalog-to-digital converters 322, 332, controller 324, blanking 326,gating 328, and detection and timestamping 330.

In operation, and as exemplified by connections 336, the power supplycurrents of amplifiers 306, 314, and 318 are integrated and coupled toanalog-to-digital converter 332. The integration of the power supplycurrents form received signal strength indication (RSSI) signals. Inaccordance with an aspect of the present invention, one or more receivedsignal strength indication signals are used over time to detect radar.More specifically, when receive path 338 receives a signal, and areceived signal strength indication signal greater than a threshold, forexample, greater than −64 dBm, is indicated, detection and timestamping330 stores or records the event in memory. For example, the event inmemory can be stored as four consecutive 16-bit words. Further, thelower two words can record information as to the type of event, alongwith other information, while the upper two words are an actual 32-bit(rollover) timer count at the time of the event. Controller 324 isoperational to process events stored or recorded in memory to detectradar as will be described hereinafter. Blanking 326 and gating 328 isused for times when access point 300 is either transmitting or receivingpacket data such that transmitted and received packeted data is notrecorded.

Referring to FIG. 4, a depiction of a typical signal 400 indicating theoperation of access point 300 shown in FIG. 3 is illustrated. Accesspoint 300 is generally capable of receiving signals ranging in magnitudebetween approximately −94 and −20 dBm, as generally indicated on theordinate or y-axis. Signals greater than −20 dBm typically overdrive orsaturate the receive path 338 of access point 300. Time is generallyindicated on the abscissa or x-axis. Those of ordinary skill in the artwill appreciate that the present invention applies equally well toaccess points having differing receive sensitivities.

As mentioned, signal 400 includes portions 402, 404 in which accesspoint 300 is transmitting and receiving packeted data, respectively. Itwill be appreciated that portions or packets 402, 404 need not haveamplitudes equaling −64 dBm; rather, this amplitude was merely forconvenience and purposes of illustration. Transmitted and receivedpacket data is generally between approximately 24 microseconds and 1.5milliseconds in duration. During those periods 402, 404, receive path338 is effectively blanked. It will be appreciated that, in someembodiments, much of the same receive path 338 is used for both radardetection and packet reception. In these embodiments, only the radardetection path is blanked while the access point receives packets.

It will be appreciated that access point 300 includes accommodations fordistributed coordinate function interframe space (DIFS) and randombackoff; in which case, the periods for transmitting and receivingpacketed data vary. Further, access point 300 can include accommodationsfor a “quiet period” before, during, or after the transmission of eachpacket.

Between transmitting and receiving packeted data, access point 300“listens” for radar during clear channel assessment (CCA) using receivepath 338. Exemplary periods for listening or clear channel assessmentare generally indicated at reference numerals 406 and 408, while adetected radar spike or signal is indicated at reference numeral 410.Typically, a radar signal 410 is a pulse of approximately 4 microsecondsin duration; however, pulses as long as hundreds of microseconds areknown.

In order for a radar signal to be detected, the signal exceeds athreshold. For example, radar signal 410 exceeds a threshold of −64 dBm,as generally indicated by arrows 412 and 414. Those of ordinary skill inthe art will appreciated that such a threshold can be set to anyappropriate power level as desired.

Referring to FIG. 5, a temporal plot 500 of the operation of accesspoint 300 shown in FIG. 3 is illustrated. Generally, time is indicatedon the abscissa or x-axis and power or magnitude is indicated on theordinate or y-axis. More specifically, temporal plot 500 showstransmitted and received packeted data 502, 504, respectively, and aseries of periodic radar bursts or pulses 506, 508, 510, 512, 514, etc.As shown in dashed line at reference numeral 516, radar pulses 506, 508,510, 512, 514, etc. are subject to some “jitter” or variation in time.In accordance with one aspect of the present invention, such jitter isallowed for in the detection of radar through “binning” as will be shownhereinafter.

In detecting a radar signal, received signal strength indication eventsduring the transmission or reception of packeted data are ignored.Further, pulses that are either too narrow or too wide are ignored, asare pulses with too much width variation. An exemplary pulse that iseither too narrow or too wide or has too much width variation is shownat reference numeral 518. Thus, transmitted and received packeted data502, 504 and exemplary pulse 518 are eliminated from spectrogram 500. Itwill be appreciated that radar pulse 512 is also effectively eliminatedalong with received packeted data 504. As will be shown hereinafter,despite eliminating radar pulse 512, the present invention is stillcapable of detection the operation of a radar system.

Once transmitted and received packeted data 502, 504, pulse 512, andexemplary pulse 518 are eliminated, the intervals between radar pulses506, 508, 510, 514, etc. are designated as A1, A2, B, and A3,respectively. It will be appreciated that intervals A1, A2, and A3 aresimilar, while interval B is longer due to the elimination of pulse 512with packeted data 504. In accordance with another aspect of the presentinvention, intervals between pulses that are either too narrow or toowide are discarded; as such intervals are not generally indicative of aradar signal.

Referring to FIG. 6, a histogram 600 is built in memory using theintervals. Such a memory is advantageously included in applicationspecific integrated circuit 334 or as part of controller 324, both ofwhich are shown in FIG. 3. In other embodiments of the presentinvention, a memory external to an application specific integratedcircuit or a controller can be used.

More specifically, histogram 600 includes a plurality of bins, e.g.,bins 602, 604, denoting the interval between two pulses arranged alongthe abscissa or x-axis. Bins 602, 604 generally cover a range ofintervals such as, for example, 200-250 microseconds and 400-500microseconds, respectively. The number of occurrences, e.g., a “bincount”, of an interval between two pulses falling in a range isindicated on the ordinate or y-axis. Those of ordinary skill in the artwill appreciate that any number of bins having any desired ranges may beused.

As shown, intervals A1, A2, B, A3 have been binned. Thus, bin 602contains intervals A1, A2, and A3, and bin 604 contains interval B. Oncethe count within one or more bins 602 exceeds are particular bin count606, access point 300 discontinues use of that frequency or channelassociated with those pulses and engages in dynamic frequency selection(DFS), thereby utilizing another available channel. Those of ordinaryskill in the art will appreciate that a bin count 606 may be adjusted asdesired to change when or how quickly a radar signal is detected.

For example, one criterion that can be used to detect a radar signal isthat if fewer than a particular number of bins are populated withintervals and if any of the bin counts are greater than some number,dynamic frequency selection is engaged. Such a criteria prevents falsedetections of radar. It has been found that if closely spaced bins haverespective bin counts that follow a Gaussian distribution, a radarsignal is not present; but rather, the access point 300 is detecting itsown transmissions. Thus, closely spaced bins having bin counts thatfollow a Gaussian distribution should be ignored. In such an instance,the bins 602, 604, should purged, reset, or cleared. Similarly, the bins602, 604 can be cleared periodically or once a radar signal has beendetected.

Referring to FIG. 7, a functional block diagram of an access point 700(e.g., access points 104 a-n illustrated in FIG. 1) in accordance withprinciples of the present invention is shown. More specifically, accesspoint 700 includes a receive path 702 for receiving packeted data on areverse link channel and a transmit path 704 for transmitting packeteddata on a forward link channel. Receive path 702 comprises antenna 706,low noise amplifier 708, frequency conversion process 710,analog-to-digital (A/D) converter 712, and physical interface (PHY)controller 714. Receive path 702 further comprises an automatic gaincontrol (AGC) circuit 716 providing receive signal strength feedbacksignals. Similarly, transmit path 704 comprises physical interfacecontroller 714, digital-to-analog (D/A) converter 718, frequencyconversion process 720, power amplifier 722, and antenna 724. Physicalinterface controller 714 selects between receive path 702 and transmitpath 704 using switches 726, 728, as indicated at reference numeral 730.A local oscillator 732 is used to select transmit and receive channels.

Physical layer interface controller 714 is advantageously an applicationspecific integrated circuit and runs off of a clock, such as, forexample, a 40 Megahertz clock (not shown). In other embodiments,physical layer interface controller 714 can include analog-to-digitalconverter 712 and digital-to-analog converter 718. Further, physicallayer interface controller 714 performs modulation/demodulation.

Physical layer interface controller 714 is coupled to media accesscontroller (MAC) 734, processor 736, and network 738. Media accesscontroller 734 is likewise advantageously an application specificintegrated circuit. Network 738 is fixed backbone network, such as fixedbackbone network 106 shown in FIG. 1.

Processor 736 controls functions of access point 700, such as, forexample, transmissions and receptions associated with a wireless link.Processor 736 is coupled to receive and transmit paths 702, 704 andlocal oscillator 732 and executes stored program code found in memory740. Processor 736 is thus programmed to record and/or manage detectedradar signals and to select communications channels for transmissions onforward, and by inference client return, links to prevent interferencewith radar systems in various ways depending upon its stored programcode. As will be appreciated by those of ordinary skill in the art, aprocessor suitably includes a memory in alternative embodiments. In yetother embodiments, a memory is external to or not a part of access point700. Processor 736 detects a radar signal by recording energy events,calculating temporal differences in recorded energy events to determinethe presence of pulses, sorting intervals between pulses into histogrambins, each bin representing a range of time intervals between twopulses, each pulse indicative of a radar frequency, and limiting networktraffic on a radar frequency based on a selected bin count.

In view of the foregoing structural and functional features describedabove, methodologies in accordance with various aspects of the presentinvention will be better appreciated with reference to FIG. 8. While,for purposes of simplicity of explanation, the methodology of FIG. 8 isshown and described as executing serially, it is to be understood andappreciated that the present invention is not limited by the illustratedorder, as some aspects could, in accordance with the present invention,occur in different orders and/or concurrently with other aspects fromthat shown and described herein. Moreover, not all illustrated featuresmay be required to implement a methodology in accordance with an aspectof the present invention. In addition, methodologies of the presentinvention can be implemented in software, hardware, or a combination ofsoftware and hardware.

Referring now to FIG. 8, a flowchart illustrating the program flow of amethod 800 for a radar protection device for wireless networks is shown.The method 800 begins by recording, e.g., detecting, timestamping and/orlogging, energy events in block 802. As used herein, energy eventsinclude, among other things, transmissions from radar systems, such asradar system 110 shown in FIG. 1.

For example, energy events are suitably recorded by receive path 338responsive to controller 334, shown in FIG. 3 or receive path 702responsive to processor 736, shown in FIG. 7. More specifically, energyevents having an energy level rising above a specified threshold and anenergy level falling below the specified threshold are recorded.Referring to FIG. 2, such a specified threshold is generally indicatedat reference letter T. Moreover, such rising and falling events aboveand below specified threshold T correspond to the leading and trailingedges of pulses 202 as generally indicated by reference numerals 210 and212, respectively. Similarly, a radar signal 410 exceeding a thresholdof −64 dBm, as generally indicated by arrows 412 and 414, is shown inFIG. 4.

Still referring to FIG. 8 and at block 804, temporal differences in therecorded energy events are calculated to determine the presence ofpulses. For example, the difference in time-stamps between correspondingportions, e.g., leading edges, of pulses 506, 508, 510, 514, etc. areused to calculate intervals A1, A2, B, A3, as shown in FIG. 5. At block806, intervals between pulses that fall outside a range, e.g., eithertoo narrow or too wide, are discarded as such intervals are notgenerally indicative of a radar signal.

At block 808, the intervals between pulses are sorted into a histogramincluding a number of bins. Each bin of the histogram represents a rangeof time intervals between two pulses. FIG. 6 shows an exemplaryhistogram 600. Accumulations in a single bin of the histogram representintervals that have a periodicity within a margin of error equal to therange of the bin.

At block 810, the histogram is periodically reset, i.e., allaccumulations in any bins of the histogram are discarded. For example,all of the bins are suitably reset once approximately every one hundredmilliseconds. Alternatively, the oldest entries in the bins are purged,such as those older than, for example, 750 milliseconds. Any bin of thehistogram exceeding a specified bins count, e.g., bin count 606, shownin FIG. 6, within the reset period indicates the presence of a number ofsimilarly spaced pulses correlating to a high probability that a radarsignal has been received. Generally, periodically resetting or purgingold entries from the bins prevents false detections of radar signals.

At block 812, and using the bin count in the histogram as an indicationof radar detection, transmission of interfering wireless network trafficis limited or ceased on the frequency that is detected, thereby reducingor eliminating interference with the radar system. To distinguish radarsystem transmissions from random high frequency pulses, wireless networktraffic is ceased when the measurement intervals between pulses areconcentrated in a small number of histogram bins, and thusly,uncorrelated detection is isolated from correlated binning due to radarperiodicity. The method 800 ends in block 814.

In order for a wireless network to successfully share the spectrum withradar systems, a radar signal must be detected quickly, efficiently, andaccurately. The foregoing method requires relatively low computationalprocessing when compared with methods that use Fourier or PeriodicTransforms, and results in high detection rates and low false alarmrates. Further, the foregoing method is robust in the presence ofuncorrelated detection noise and is easily parameterized to account fordifferences in radar systems.

By virtue of the foregoing, there is thus provided a radar protectiondevice and method that addresses the regulatory requirements and allowsthe co-existence of a wireless network with radar systems.

While the present system has been illustrated by the description ofembodiments thereof, and while the embodiments have been described inconsiderable detail, it is not the intention of the applicants torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. It will be understood that the presentinvention is applicable to any wireless network using packeted data.Moreover, such a network is not limited to operation in any particularfrequency band; but rather, may operate at any frequency as desired.Further, the invention is not limited to operation in accordance withany standard or regulations. Therefore, the invention, in its broaderaspects, is not limited to the specific details, the representativeapparatus, and illustrative examples shown and described. Accordingly,departures may be made from such details without departing from thespirit or scope of the applicant's general inventive concept.

1. An apparatus, comprising: a circuit for receiving a wireless signal;and a processor coupled to the circuit and operable to select anoperating frequency for the circuit; wherein the processor is configuredto record energy events received by the receiver on a first frequency;wherein the processor is responsive to recording the energy events todetermine intervals based on temporal differences between the energyevents; wherein the processor is configured to store counts of intervalsbetween energy events into a plurality of histogram bins, wherein eachbin represents a range of time intervals between energy events whereinthe processor is configured to determine radar is present on the firstfrequency based on one of the plurality of histogram bins having a countgreater than a predetermined threshold; and wherein the processor isconfigured to select a second operating frequency responsive todetermining radar is present on the first frequency.
 2. An apparatusaccording to claim 1, wherein the processor is configured to recordenergy events having an energy level rising above a specified thresholdand an energy level falling below the specified threshold are recorded.3. An apparatus according to claim 1, wherein the recording energyevents by the processor includes at least one of detecting,time-stamping, and logging energy events.
 4. An apparatus according toclaim 1, wherein the recorded energy events are pulses having a widthwithin a desired range.
 5. An apparatus according to claim 4, whereinthe desired range is approximately one to twenty microseconds.
 6. Anapparatus according to claim 1, wherein the processor is configured toperiodically reset the count.
 7. An apparatus according to claim 6,wherein the count is reset once approximately every one hundredmilliseconds.
 8. An apparatus according to claim 1, wherein theprocessor is configured to periodically purge the oldest energy events.9. An apparatus according to claim 8, wherein energy events older thanapproximately 750 milliseconds are purged.
 10. An apparatus according toclaim 1, further comprising: a transmitter coupled to the processor;wherein the processor is operable to select an operating frequency forthe transmitter; and wherein the processor is responsive to switch theoperating frequency for the transmitter from the first frequency to thesecond frequency responsive to determining radar is present on the firstfrequency.
 11. An apparatus according to claim 10, further comprising ablanking and gating circuit configured to detect packeted data receivedby the receiver and packeted data sent by the transmitter, wherein theprocessor is configured not to record packeted data received by thereceiver and packeted data sent by the transmitter as energy events. 12.An apparatus according to claim 1, wherein the recorded energy eventsare energy events determined not to contain packeted data.
 13. A method,comprising: recording energy events on a first frequency; calculatingintervals between recorded energy events; storing counts of intervalsbetween energy events into a plurality of histogram bins, wherein eachbin represents a range of time intervals between energy events;determining radar is present based on one of the plurality of histogrambins having a count greater than a predetermined threshold; andselecting a second frequency responsive to determining radar is present.14. A method according to claim 13, wherein the recorded energy eventsare energy events determined not to contain packeted data.
 15. A methodaccording to claim 13, wherein recording energy events comprises one ofa group consisting of detecting energy events, time-stamping energyevents, and logging energy events.
 16. A method according to claim 13,wherein the recorded energy events have a pulse width within apredetermined range.
 17. A method according to claim 13, furthercomprising resetting the count after a predetermined time interval.